26 January 2026: Ocean Circulation and Climate Dynamics Colloquium

When?  Monday 26 January 2026 at 11 am
Where?    Room 8A-208, Wischhofstr. 1-3 and online
via Meeting link:https://geomar.webex.com/geomar-en/j.php?MTID=ma73a9dd4db0f5cb6275b471e1c5e6005

Meeting number: 2789 008 5026
Password: nhPGUfGj553

Abstract:
The downward limb of the AMOC is not well understood, partly due to discrepancies between the Eulerian perspective and the isopycnal water-mass perspective. Using km-scale global coupled ICON simulations, we investigate how water volume is transferred from the upper to the lower AMOC limb, and we reconcile transports diagnosed in density and in depth spaces. We find that the volume transport into the lower limb is operated by subduction from the mixed layer at the locations where the isopycnal of the maximum stream function outcrops. This transport is concentrated between the Irminger Gyre and the Irminger Current and along the Eastern Greenland Current, where steep isopycnals trigger baroclinic and barotropic instabilities, producing mesoscale eddies that subduct upper dense water into the lower limb and carry lower light water to the upper limb. Seaward of current fronts, the eddy-induced transport dominates; shoreward of current fronts, the time-mean transport dominates. We further establish the connection between the interface velocity defined at isopycnal layers and the Eulerian vertical velocity defined at fixed depth. The fundamental difference between volume transports diagnosed in density space versus depth space arises from horizontal subduction and eddy-induced subduction, which are only accounted for in the isopycnal framework. We conclude that the interface velocity well captures the nonlinear, eddy-rich pathways feeding the lower limb of the AMOC.

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